Converter system



April 30, 1940. P. J. WALSH 2,199,121

CONVERTER SYSTEM Filed Jan. 18, 1938 \al I 6 4 AL 7 T a a Z 24- a 3 6 ai PULL Patented Apr. 30, 1940 UNITED STATES CONVERTER SYSTEM Philip JohnWalsh,

San Francisco, Calif.

Application January 18, 1938, Serial No. 185,528

6 Claims.

This invention relates to a system for converting alternating currentinto direct current. In connection with electrochemical processes,

arc welding, radio transmitters and receivers,

and many other devices, the electric power is usually supplied asalternating current which must be changed to direct current before itcan be utilized. At the present time this is done by means ofrectiflers, heavy motor-generators or other mechanical movingcontactors.

It has been found that such rectifiers are expensive, ineflicient andmust be renewed frequently, and in electrochemical processes wheredirect currents of several thousand amperes are employed, the heavymotor driven generator is practically the only means of convertingalternating current power into direct current.

It is one of the objects of my invention to obviate these disadvantages,and to provide a simple scheme for obtaining a high degree ofefllciency.

It is another object of my invention to obtain this high degree ofefficiency without theme of moving parts.

It is still another object of my invention to provide an inexpensiveconverter system that operates over a long period of time withoutattention.

My invention possesses many other advantages and has other objects whichmay be made more easily apparent from a consideration of one embodimentof my invention. For this purpose, I have shown a few forms in thedrawing accompanying and forming part of the present specification. Ishall now proceed to describe these forms in detail, which illustratesthe general principles of my invention; but it is to be understood thatthis detailed description is not to be taken in a limiting sense, sincethe scope of my invention is best defined by the appended claims.

Referring to the drawing:

Figure 1 is a schematic wiring diagram of one form of my invention;

Figure 2 is a diagram for facilitating explanation of the invention;

Figure 3 is a wiring diagram of a still further modification.

I show a source of alternating current I which may be an alternator orany other source of current, connected to the primary coil 2. of atransformer comprising the coils 2 and I wound on the iron core 3. Thesecondary coil 4 has the two end terminals 5 and 1 and a center tap 6.Alternating current flowing in the primary coil 2 causes anelectromotive force to be induced in the secondary coil 4 by transformeraction. Since the operation of such a transformer is now well understoodfurther detailing thereof is unessentlal, except to point out thatduring one half cycle when terminal 5 is positive I and terminal Inegative, tap 8 is negative relative to terminal 5 and positive relativeto terminal I. But during the other half of the cycle when terminal 5 isnegative and terminal I positive, tap 6 is positive relative to terminal5 and 1. negative relative to terminal I.

When terminal 5 is positive current flows through the circuit made up ofconnection 8,'coil I0 wound on the core of magnetic material l5,connection 2|, coil I wound on the core of magnetic material I6 andconnection 8 back to the negative terminal I. The current flows in theopposite direction in this circuit when terminal I is positive andterminal 5 negative, that is, from terminal I, connection 9, coil H,connections 29 and 2|, coil l0 and connection 8 back to the negativeterminal 5. The coils I0 and it are made of the same number of turns andhave substantially the same impedance. Now it is seen that without meansto unbalance these equal coils there is no difference of potentialbetween tap 6 and point 22, and therefore no current flow between thesetwo points. As the description proceeds I will explain how the coils I0and II are made to unbalance the circuit during each half cycle so thatcurrent flows, in one direction only, from tap 6 through coil 23 andconnection 24 to point 22.

The field coils I I and I2 wound on the cores I5 and I6 respectively,are for the purpose of polarizing the cores. Current from the battery l8flows through connection 25, contact 26. arm 21, connection 28, arm 20,resistor I9, coil -Il, choke coil II, coil I2 and back to battery l 8This current flowing in the coils II and I2 sets up a magnetic flux inthe cores I5 and IS in the direction of the full line arrows. Thestrength of this current, that is, the magnetizing force expressed inampere turns and the resulting magnetization or magnetic flux throughthe cores can be controlled by adjusting the resistor I9.

In Figure 2, I show a typical B-H curve for iron, which shows therelation between the magnetlzing force H, and the resulting magneticflux B, through the core. It is seen that B increases as H is increasedup to the point e, on the curve, after which any further increase in Hhas little effect on B. This is known as the v saturation pointthe ironbecomes magnetically saturated.

If the magnetization of the iron is brought to the point a on the curve,by adjustment 01 resistor l9, equal increments and decrements added tothe magnetizing force (caused by alternating current flowing in the coilIII or coil it) cause the magnetic flux in the core to increase duringthe positive half of the cycle by the small amount c-d on the curve. Butduring the negative half of the cycle the magnetic flux in the core willbe reduced by the considerably larger amount a-b. Now it is apparentthat by proper adjustment of resistor 9, Figure l, the cores l5 and Itcan be magnetically saturated by the current flowing in the coils II andi2. Under such circumstances current flowing in coil ID or in coil It insuch a direction as to further magnetize the core can causesubstantially no change in the magnetic flux therein: but when currentflows in either coil in or coil It in the opposite direction, tending todemagnetize the core, there is a large change in the strength of themagnetic flux in the core.

It thus comes about that during the positive half cycle coil in actslike a coil wound on an iron core while coil it acts like a coil withoutan iron core. During the negative half of the cycle the actions arereversed, that is, coil ll acts like a coil with an iron core while coili acts like a coil without an iron core. The choke coil I1 which doesnot oppose the flow or direct current through itself from the batteryl8, offers an extremely high impedance to alternating currents inducedin the coils II and I2 by the variations in the magnetic flux in thecores i and I6, and thus substantially prevents the flow of alternatingcurrent through the battery l8.

When the cores l5 and I8 are properly polarized by direct currentflowing in the coils H and I2, the-circuit including the coils l0 and II is no longer balanced, and therefore a difference of potential existsbetween tap 6 and point 22. Because now when terminal 5 is positive andterminal 1 negative during one half cycle, current flows through coil l0in a direction tending to demagnetize the core l5, thus causing a largechange in the magnetic flux therein. As this current builds up from zeroto maximum the flux is reduced from its normal value to its minimumvalue, and when this current gradually falls away to zero, the fluxbuilds up to its normal steady value. This change in the flux causes acounter electromotive force to be induced in the coil ID in such adirection as to oppose the flow of current therethrough, But the currentflowing through the coil N tends to further magnetize the core, andtherefore there is substantially no change in the magnetic flux, andsubstantially no counter electromotive i'orce generatedtooppose the flowoi current therein. Now as tap 3 is also positive relative to terminal 1current flows from tap 3 through coil 23, connection 24 to point 22,connection 23, through coil H in a direction tending to furthermagnetize the core i3, connection 3 and back to the negative terminal 1.

During the other half of the cycle when terminal 1 is positive andterminal 5 negative, current flows from terminal 1, connection 3, coil Inow in a direction tending to demagnetize the core l3, connections 23and 2|, through coil Hi now in a direction tending to further magnetizethe core I, connection 3 and back to the negative terminal 3. Thus thecurrent flowing in coil It generates a counter electromotive iorce whichopposes it, but substantially no opposing force is generated in coil l3.At the same time tap 3 is positive relative to terminal 3 and currentflows from tap 6 through coil 23, connection 23 to point 22 in the samedirection as before, connection 2|, through coil ii in a directiontending to further magnetize the core, connection I and back to thenegative terminal 3.

Thus it is seen that during each cycle two hall waves of current flowfrom point 3 to point 22 in one direction only, which constitutes adirect current. Also that this current is always flowing in such adirection through either the coil ill or the coil H as to tend tofurther magnetize the cores, thus no opposing force is generated.

When the direct current flowing through the coil 23 builds up to apredetermined value, the relay arm 21 snaps over rapidly from thecontact 23 to the contact 3|. This relay is arranged for fastsnap-action and is held in the position shown by a spring, the arm 21 isdrawn over to the other position by the magnetic pull of core 33 whencurrent flows in the coil 23. When the arm snaps into contact withcontactor 3|, the battery I3 is cut out of the circuit and directcurrent flows from tap E, contactor 3|, relay arm 21, connection 28,resistor arm 20, resistor I9, coil il, choke coil l1, coil i2,connection 32, connection 23 to point 22. The coil 23 is connectedacross the direct current output terminals 33 and 34. The battery i3 isused for starting purposes only and any other convenient source ofdirect current can be used for this purpose instead of the battery. Whenswitch 35 is closed, the direct current load I3 is connected to theoutput terminals 33 and 33 as shown.

The coils HI and it are designed to have a high inductive reactance andlow resistance so as to reduce the flow of circulating current, throughboth coils i0 and II, between the terminals 3 and I, and thus increasethe efliciency of the system. This circulating current can be furtherreduced, to value that is vanishingly small, by means of the condenser31. The capacity reactance of condenser 31 is made equal to theinductive reactance of the coils Ill and it connected as shown, so thatwhen switch 33 is closed, the condenser 31 cooperates with the coils inand I to form a parallel resonant circuit between the terminals 5 and 1.

I will now explain how the condenser 31 cooperates with the coils iiiand II to oppose the flow of circulating current through the circuitconnected between the terminals 5 and 1.

Let us assume that at this instant the condenser 31 is fully charged,and in such a direction as to make its upper terminal positive and itslower terminal negative. With the switch 36 closed. condenser 31discharges through the path, coil I 0, connections 2| and 23, coil l4,connection 3, switch 33 and back to condenser 31, in the directionindicated by the broken line arrows. This current flowing in the coil l0reduces the strength of the magnetic flux in the core I! but hassubstantially no eflect on the flux in core I because it flows in adirection through coil ll tending to further magnetize the core l3.

As the fluxin core I3 builds up to its normal steady value it causes anelectromotive force to be induced in the coil ill of such a direction asto send a current through the path, coil i3, connections 2| and 23, coilll, connection 3, switch 33, condenser 31 and connection 3 to coil it,in the direction indicated by the broken line arrows and charge thecondenser in the opposite direction in the core It builds back up againto its normal value it causes an electromotive force to be induced incoil 14 which sends a current in a direction opposed to the broken linearrows through the path, coil I4, connections 29 and 2|, coil 10,connection 8, condenser 31, switch 36, and coil 14, and chargescondenser 31 in the opposite direction, that is, making its upperterminal positive and its lower terminal negative.

Thus while condenser 31 is cooperating with one of the coils It) or l4to form a. parallel resonant circuit to oppose the flow of circulatingcurrent through the circuit between the terminals 5 and 1, current flowswithout opposition from tap 6 and through the other coil to one of theterminals 5 or I. The phase relations by proper connection could readilybe shown to be such as to affect this result. Since the operation of aparallel resonant circuit is now well understood further detailingthereof is unessential, except to state that at any instant a voltage isset up by either the condenser or the coil that is substantially equalto, and opposed to, the applied voltage.

When the system is operating from a commercial cycle alternating currentsource and producing direct currents of several thousand amperes, thecoils l0 and I4 can be made of a few turns of heavy copper conductorwound on relatively large cores, and the capacity of condenser 31 can bemade such that its capacity reactance is equal to the effectiveinductive reactance of the coils connected as shown.

The cores l5 and I6 can be made of iron,

nickel, permalloy or other magnetic material, and

when the device is operating at high frequency, they can be made offinely divided particles of these materials mixed with a binder andpressed into the desired shape. The cores can be polarized by means ofpermanent magnets instead of the magnetizing coils II and 12.

In Figure 3, the cores 38 and 39 made of magnetic material can beclamped onto the permanent magnets 40 and 4| having north N, and southS, poles as shown in the drawing. The operation of this form of theinvention is practically the same as the form shown in Fig. 1, exceptthat the starting source such as battery I8, and the coils II and 12,are not necessary. The condenser 46 and the coils 42 and 43 operate inthe same manner as the condenser 31 and the coils l0 and I4 of Fig. 1.The input transformer comprlsingthe coils 41 and 48 wound on the core49, corresponds to the coils 4 and I wound on the core 3 of Fig. 1.

This form of the invention is best adapted to operate at high frequency,or at high voltage where a small current represents a large power value,

The condensers 31 and" can be made variable so that they can be adjustedto the point of most efllcient operation. I

The direct current load circuit shown as the coil 45 and the resistor 44corresponds to the direct current load l3 of Fig. 1.

I claim:

1. In a parallel resonant circuit having a pair of coils wound on coresof magnetic material, the coils being connected together and shunted bya condenser, the process which comprises magnetizing the cores in such adirection as to cause substantially only one of the coils to act as aninductance and cooperate with said condenser to form a parallel resonantcircuit and the other coil to act substantially as a resistance during apart of each cycle, and reversing the actions of both coils during theremainder of each cycle.

2. The system as set forth in claim 1, with the addition or meansincluding a permanent magnet for magnetizing the core.

3. In combination means forming a parallel resonant'circuit comprisingcoils wound on cores of magnetic material, the coils being connectedtogether and shunted by a condenser, and means for magneticallypolarizing said cores associated and cooperating therewith whereby thecurrent surging between said condenser and the coils causes theelectrical properties of each coil to vary simultaneously oppositely tothe other coil.

4. In a converter, two coils wound on mag netized cores, a connectionbetween said coils, a condenser bridging said coils, an alternatingcurrent input circuit having a center tap, connections from the ends ofsaid coils to said input circuit, a direct current load circuitconnected between the center tap and the connection be tween said coils,the process which comprises magnetizing the cores in such a direction asto cause the coils to cooperate with the condenser to form a parallelresonant circuit to prevent the flow of a substantial circulatingcurrent from said input circuit, while allowing current to flow fromsaid center tap through the coils.

5. The system as set forth in claim 4, with the I addition of apermanent magnet for magnetizing PHILIPJOHN WALSH.

